1. Field of the Invention
This invention relates generally to circuit boards and more particularly to a material construction for use in Etched-Tri-Metal, xe2x80x9cETMxe2x80x9d, multi-layer circuit boards.
2. Description of the Related Art
In the field of electronics manufacturing, various additive and subtractive processes that are known for constructing printed circuit boards (PCBs). Among these are the processes disclosed in U.S. Pat. No. 3,801,388 issued Apr. 2, 1974 to Akiyama et al. which is a subtractive process. U.S. Pat. No. 4,404,059 issued Sep. 13, 1983 to Livshits et al is an additive process. U.S. Pat. No. 5,738,797 issued Apr. 14, 1998 to Belke, Jr. et al is assigned to a common assignee. All three of which are incorporated herein by reference. These patents describe various additive and subtractive plating and chemical etching processes for constructing multi-layer PCBs having air bridges.
A method for cladding material for etched-tri-metal circuits to maintain the dimensional tolerance and reducing the stresses in the cladded material having the steps of first forming a stacked set of tri-metal material having three layers of metal. The central layer is one material, which is aluminum, and the top and bottom layers are a second material, which are copper.
Then each set of the tri-metal material have the outside surfaces of the top and bottom layers oxidized to prevent the sets from adhering together when they are stacked. Prior to being stacked, each set is fed through a cladding mill having a predetermined pressure and temperature. After exiting the cladding mill, the individual sets of the tri-metal material are stacked with the oxidized surfaces abutting each other.
Then the stacked sets are processed through a rolling mill at a predetermined pressure and temperature to reduce the thickness of the multiple set of tri-metal cladded material. After finishing rolling, the multiple set of tri-metal cladded material is separated into the individual sets of tri-metal material.